1. Field of the Invention
The present invention is generally related to a carrier phase and symbol timing recovery circuit used for a High Definition Television (HDTV) receiver operating in accordance with a standard of the Advanced Television System Committee (ATSC), and to a method of recovering a carrier phase and a symbol timing in received digital signal data.
2. Description of the Related Art
ATSC receiving systems may be designed to operate even in severe multi-path environments, such as cities for example. In multi-path environments, substantially strong ghost signals may occur due to reflection of electromagnetic waves from buildings, etc. Therefore, in order to operate stably in severe multi-path environments, ATSC receiving systems should have substantially robust carrier phase and symbol timing recovery circuits and/or processing schemes.
In order to increase bandwidth efficiency in a digital transmission system and the ATSC 8 Vestigial Side Band (VSB) transmission system proposed in accordance with the North America digital television (DTV) transmission standard, only data signals are carried on a transmission signal. In other words, transmission sides do not transmit clock information used for data recovery. Therefore, reception sides should generate clocks similar to those used by the transmission sides in order to recover data from received signals which contain only data. The process is performed by what is referred to as a timing recovery unit. In addition, in order to recover transmitted data, it is desirable to accurately generate the phase of the carrier transmitted at the time of recovering carrier-removed data from the received data. The process is performed by what is referred to as a carrier phase recovery unit.
In general in the conventional art, carrier phase and symbol timing recovery processes may be performed separately. In addition, a phase locked loop (PLL) may be used for the carrier phase recovery process, and a segment synchronization-based algorithm or a Gardner algorithm may be used for the symbol timing recovery process. The Gardner algorithm uses redundancy information in what is referred to as an upper overlapped region.
On the other hand, ATSC receiving systems are based on offset-modulation formats. Therefore, it may be substantially difficult to design a phase recovery circuit which does not depend on a symbol timing offset. Similarly, it is not possible to design a symbol timing recovery circuit completely independent of a phase offset.
Conventionally, several approaches have been used for avoiding complicated correlation between carrier phase and symbol timing recovery circuits. For example, carrier phase and symbol timing recovery circuits may be used in respective wide and narrow bands in order to stabilize the associated operations of ATSC demodulators. However, it is difficult for conventional recovery circuits to completely separate the carrier phase recovery process from the symbol timing recovery process.